Parallel Line Resonance Between Interagency Transmission Lines and the Effect on a De-Energized Line with Fixed Shunt Reactance

Event analysis is a staple of system protection, yet it is easily hindered by limited and lacking data. This is especially relevant at points of utility interconnection as interagency cooperation is necessary for robust fault analysis. Even so, protection engineers are expected to reach reasonable conclusions about unexpected operations which can be particularly difficult when power system phenomena like parallel line resonance is involved. In this particular case, a permanent phase-to-ground fault demonstrated a correlation between a shunt reactor and the capacitive coupling between two transmission lines in the same right of way that interconnect multiple utilities and electrical systems. As is demonstrated, the utility proposed theory of the mutual coupling inducing zero sequence current on the de-energized line was inaccurate as a diagram of the zero sequence network reveals a missing zero sequence voltage source. Instead, the phase-to-ground fault formed a zero sequence resonant network between the shunt reactor inductance and the de-energized line capacitive coupling. This circuit was then excited by circulating zero sequence current and sustained by zero sequence voltage induced from the adjacent, energized, parallel line. Analysis of this resonant circuit shows the potential for extremely high induced voltage magnitudes which are governed by the topography and geometry of both parallel lines and location of the phase-to-ground fault.